fix bugs

src/classes/magic_stone.py

@@ -11,9 +11,11 @@ class MagicStone(int):
         self.value = value
 
     def exchange(self) -> tuple[int, int, int]:
-        _value, _upper = divmod(self.value, 100)
-        _value, _middle = divmod(_value, 100)
-        return _upper, _middle, _value
+        # 期望顺序：返回 (上品, 中品, 下品)
+        # 汇率：100 下品 = 1 中品；100 中品 = 1 上品
+        _middle_total, _lower = divmod(self.value, 100)
+        _upper, _middle = divmod(_middle_total, 100)
+        return _upper, _middle, _lower
 
     def __str__(self) -> str:
         _upper, _middle, _value = self.exchange()
@@ -24,7 +26,21 @@ class MagicStone(int):
             return MagicStone(self.value + other)
         return MagicStone(self.value + other.value)
 
+    def __iadd__(self, other: Union['MagicStone', int]) -> 'MagicStone':
+        if isinstance(other, int):
+            self.value += other
+        else:
+            self.value += other.value
+        return self
+
     def __sub__(self, other: Union['MagicStone', int]) -> 'MagicStone':
         if isinstance(other, int):
             return MagicStone(self.value - other)
-        return MagicStone(self.value - other.value)
+        return MagicStone(self.value - other.value)
+
+    def __isub__(self, other: Union['MagicStone', int]) -> 'MagicStone':
+        if isinstance(other, int):
+            self.value -= other
+        else:
+            self.value -= other.value
+        return self